mojo: Allow basic RunLoop to be quit from a posted task.

mojo/public/cpp/utility/tests/run_loop_unittest.cc

Index: mojo/public/cpp/utility/tests/run_loop_unittest.cc
diff --git a/mojo/public/cpp/utility/tests/run_loop_unittest.cc b/mojo/public/cpp/utility/tests/run_loop_unittest.cc
index d9f754c66d3fde8245fbc03651a34a5a1829ff36..e11c4188d701e0556c66f517816a1a5f396912cb 100644
--- a/mojo/public/cpp/utility/tests/run_loop_unittest.cc
+++ b/mojo/public/cpp/utility/tests/run_loop_unittest.cc
@@ -413,5 +413,42 @@ TEST_F(RunLoopTest, DelayedTaskOrder) {
   EXPECT_EQ(3, sequence[2]);
 }
 
+struct QuittingTask {
+  QuittingTask(RunLoop* run_loop) : run_loop(run_loop) {}
+
+  void Run() const { run_loop->Quit(); }
+
+  RunLoop* run_loop;
+};
+
+struct ClosingTask {
+ public:
+  ClosingTask(ScopedMessagePipeHandle* handle): handle(handle) {}
+
+  void Run() const {
+    handle->reset();
+  }
+
+  ScopedMessagePipeHandle* handle;
+};
+
+TEST_F(RunLoopTest, QuitFromDelayedTask) {
+  TestRunLoopHandler handler;
+  MessagePipe test_pipe;
+  RunLoop run_loop;
+  run_loop.AddHandler(&handler,
+                      test_pipe.handle0.get(),
+                      MOJO_HANDLE_SIGNAL_READABLE,
+                      MOJO_DEADLINE_INDEFINITE);
+  run_loop.PostDelayedTask(Closure(QuittingTask(&run_loop)), 0);
+  // Ensure the test won't block forever.
+  run_loop.PostDelayedTask(Closure(ClosingTask(&test_pipe.handle1)), 1e5);

[jamesr, 2014/09/22 22:30:18]

hmm, 1e5 microseconds = 100ms if i'm not mistaken. On a noisy system, we could
definitely have gaps of larger than this unaccounted for

+  const MojoTimeTicks before = GetTimeTicksNow();
+  run_loop.Run();
+  const MojoTimeTicks after = GetTimeTicksNow();
+  // Check that the run loop did quit before the closing task was run.
+  ASSERT_LE(after-before, 5e4);

[jamesr, 2014/09/22 22:30:18]

this is super racy. if you want tests like this we need a way to inject a fake
clock implementation.

why not just assert that we exited (i.e. that the test harness didn't time out?)

[qsr, 2014/09/23 10:40:15]

 I didn't want to count on timeout because in case of error, it will delay the
CQ for a lot of time, but if this is considered OK, then yes, I can do it. It
makes the test a lot simpler.

+}
+
 }  // namespace
 }  // namespace mojo